Physics Help Forum Circuit problem

 Electricity and Magnetism Electricity and Magnetism Physics Help Forum

 May 11th 2009, 02:27 AM #1 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 Circuit problem In Figure (1) the box represents the circuit of a d.c. motor running at a steady speed. The motor behaves as a source of e.m.f. E (opposing that of the 120V battery) and an internal resistance of 4ohms. these are parallel with a 240ohm resistor. a current of 5.5A is drawn from the 120V battery with negligible internal resistance. i) calculate the current through the 4ohm resistor ii) the e.m.f. E In figure (2), the motor is not running. An extra resistor R is added to limit the current on starting. What is the resistance of R if the current is to be limited to 20A? i'm confused about the e.m.f. in the opposite direction thing. thanks Attached Thumbnails
 May 12th 2009, 03:40 AM #2 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 Solved! Yay!

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